Counter of Festivals

Ashok Blog for SQL Learners and Beginners and Experts

Wednesday, 18 December 2013

SQL CHECK Constraint in SQL Server

SQL CHECK Constraint

The CHECK constraint is used to limit the value range that can be placed in a column.
If you define a CHECK constraint on a single column it allows only certain values for this column.
If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row.

SQL CHECK Constraint on CREATE TABLE

The following SQL creates a CHECK constraint on the "P_Id" column when the "Persons" table is created. The CHECK constraint specifies that the column "P_Id" must only include integers greater than 0.
MySQL:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CHECK (P_Id>0)
)
SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL CHECK (P_Id>0),
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Sandnes')
)



SQL CHECK Constraint on ALTER TABLE

To create a CHECK constraint on the "P_Id" column when the table is already created, use the following SQL:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD CHECK (P_Id>0)
To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:
MySQL / SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ADD CONSTRAINT chk_Person CHECK (P_Id>0 AND City='Sandnes')



To DROP a CHECK Constraint

To drop a CHECK constraint, use the following SQL:
SQL Server / Oracle / MS Access:

ALTER TABLE Persons
DROP CONSTRAINT chk_Person